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MAY 1 MOUNTAIN SNOWPACK AND STREAMFLOW FORECASTS NEAR TO ABOVE AVERAGE

May 6, 2009

For More Information:
Scott Oviatt, 406-587-6844
Ivy Allen, 406-587-6971

Bozeman--Snowfall the last part of April helped the north central mountains make substantial snow water increase. Late April snow water percentage increase in the Missouri Mainstem was 13 percent. and the Missouri Headwaters percentage increase was 17 percent. West of the Divide percentage increases ranged from 4 to 9 percent. Mountain snowpack state-wide was generally near to above average and below last year. April mountain precipitation for the Columbia River Basin was 76 percent of average; Missouri River Basin was 118 percent of average; and Yellowstone River Basin was 112 percent of average.

State-wide mountain snow water contents were 110 percent of average and 89 percent of those on May first last year. Snowpack in the Columbia River Basin was 102 percent of average and 76 percent of last year, the Missouri River Basin was 116 percent of average and 100 percent of last year, and the Yellowstone River Basin was 110 percent of average and 104 percent of last year.

Snow Water Content
River Basin Percent of Average Percent of Last Year March Percent of Change
Columbia 102 76 +4
Kootenai, Montana 97 72 0
Kootenai, Canada 85 83 15
Flathead, Montana 94 70 + 1
Flathead, Canada 81 62 -4
Upper Clark Fork 117 99 +9
Bitterroot 109 77 +4
Lower Clark Fork 103 69 +8
Missouri 116 100 +16
Missouri Headwaters 118 102 +17
Jefferson 119 108 +16
Madison 113 92 +17
Gallatin 116 98 +14
Missouri Mainstem 113 97 +13
Headwaters Mainstem 121 111 +13
Smith-Judith-Musselshell 117 106 +12
Sun-Teton-Marias 104 86 +11
Milk (Bearpaw Mountains) 49 30 ---
St. Mary 80 69 + 7
St. Mary & Milk 80 68 0
Yellowstone 110 104 + 8
Upper Yellowstone 118 107 +12
Lower Yellowstone 102 101 + 6
Statewide 110 89 +10

State-wide, streamflows are forecast to average 93 to 105 percent. West of the Divide, streamflows are forecast to average 95 to 104 percent. East of the Divide, streamflows are forecast to average 92 to 107 percent of average.

Below are averaged River Basin streamflow forecast summaries for the period May 1 through July 31. These forecasts assume near normal spring conditions and do not account for well below average (70% or less) or well above average (130% or more) snowmelt or spring rain. Specific forecast probabilities are available in each individual River Basin Report.

Streamflow Forecasts
River Basin May to July this Year Percent of Average May to July Last Year Percent of Average
Columbia 95 to 104 107 to 116
Kootenai 85 to 93 115 to 126
Flathead 88 to 96  103 to 111
Upper Clark Fork 106 to 119  96 to 109
Bitterroot 98 to 107 108 to 117
Lower Clark Fork 94 to 99 124 to 129
Missouri 91 to 107 81 to 100
Jefferson 99 to 117 77 to 101
Madison 93 to 100 112 to 119
Gallatin 108 to 115 103 to 111
Missouri Mainstem 96 to 109 98 to 113
Smith-Judith-Musselshell 96 to 118 51 to 70
Sun-Teton-Marias 74 to 91 91 to 111
Milk 70 to 87 59 to 83
St. Mary 82 to 89 100 to 107
Yellowstone 95 to 107 92 to 104
Upper Yellowstone 99 to 108 94 to 104
Lower Yellowstone 90 to 105 88 to 103
Statewide 93 to 105 93 to 107

NOTE: The May-July Last Year % of Average column above is last years forecasts on May 1, not of what actually occurred.

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